A local ham friend copied this strange, wide signal on 30 meters on his Flex 5000. Anybody know what it might be?

Flex spectrogram of wide, unknown signal

  • $\begingroup$ The 30m amateur allocation in the US says to avoid interference to fixed services outside the US. I've never found specific information on what those are, but maybe this is one of them? $\endgroup$ Feb 14, 2017 at 16:28
  • $\begingroup$ @Phil Frost - W8II A well known example in Europe is the DDK9 operated by the Deutsche Wetter Dienst at 10100.8 kHz. It emits RTTY weather forecasts all day, every day. $\endgroup$
    – AndrejaKo
    Feb 14, 2017 at 19:52
  • $\begingroup$ It would be handy to know where both you and your friend are located. Lots of people are here or assuming the United States, however other places than the United States have amateur radio operators. $\endgroup$ Feb 16, 2017 at 18:39
  • $\begingroup$ @RowanHawkins SW Missouri. Look up W0BTU and W0EBV on qrz.com. $\endgroup$ Feb 16, 2017 at 20:58

2 Answers 2


If I read the instrumentation correctly, this is but 20 kHz; that's pretty wide for what I'd expect for Ham operation on HF. It's not "very wide" per se. (I'd define "wide" based on the ratio of bandwidth to center frequency, and that's but 0.2% here.)

This looks a bit like an OFDM signal, especially with the hints of side lobes. 20 kHz OFDM in HF sounds a lot like Digital Radio Mondiale.

I don't know of any specific allocation of 10 MHz spectrum to broadcast licensees. However, since there is a really good free and open source DRM transmitter, built atop of GNU Radio, named gr-drm, this might very well be legitimate Ham usage; admittedly, using the high-quality channel mode for DRM does use a lot of bandwidth compared to a classical AM voice channel, but at the same SNRs, DRM sounds worlds superior if using the right voice codecs.

In Germany, for example, 10.000 – 10.150 MHz is reserved to FESTER FUNKDIENST (fixed radio service) application with "messages to one or multiple recipients" as primary, and Amateur Radio as secondary usage. p. 94 of the Frequenzplan

  • 1
    $\begingroup$ Part §97.307(c) in the US puts some limits on occupied bandwidth for data, though I've never been able to follow all the indirection enough to really understand what the rules are. Taking 20kHz out of a band that's only 50kHz wide does seem like a dick move, especially when the entire band does not allow phone transmissions. $\endgroup$ Feb 14, 2017 at 16:27
  • $\begingroup$ @PhilFrost-W8II That's my thinking, too. I'll ask him when this occurred, which may help roughly determine how far away that station might have been. If it was from the USA, do the FCC rules allow modes like this on 30m? $\endgroup$ Feb 14, 2017 at 18:02
  • $\begingroup$ hey, looked that up in German FAT and added to the answer. $\endgroup$ Feb 14, 2017 at 18:09
  • $\begingroup$ If you can record a couple seconds of raw IQ data, you might be able to run gr-inspector on it, and let it guess the OFDM parameters. $\endgroup$ Feb 14, 2017 at 18:34
  • $\begingroup$ @Marcus Müller MHz of kHz? $\endgroup$
    – AndrejaKo
    Feb 14, 2017 at 19:53

I also didn't notice that box before, but it has the date as well, 2017-01-08 in it(YMD), a Sunday.

The center is 10.130, and at S7 that's fairly strong. Also I think the actual signal is 26khz wide with the 3khz side lobes.

I don't think its DX. At 9am the sun is well up, the ionosphere E layer has merged back into D. There would be no grey line propigation in play. I realized there is a viable alternative answer...QRM.


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